1. Technical Field
The present invention relates to a method for producing fine convexes or concaves, in particular, a method for producing surface convexes or concaves suitable for manufacturing optical materials, which comprises a transparent material having surface convexes or concaves, such as light diffusing panels, light control films and microlenses.
2. Background Art
For various optical apparatuses, screens and displaying apparatuses such as liquid crystal displays, there are used optical materials such as light diffusing films and microlenses, in which fine convexes or concaves are provided on surfaces in order to control projection directions of transmitted light or reflected light. As such optical materials, there have been proposed not only those simply having random convexes or concaves, but also those having concaves or convexes of which shapes, intervals and so forth are highly precisely defined in order to control light paths (Patent document 1).
Generally employed as techniques for providing convexes or concaves on surfaces of materials are chemical matting in which a matting agent is mixed in a layer forming a surface, embossing, impressing and so forth. However, in the chemical matting, the matting agent itself has particle size distribution, and in addition, dispersion state thereof is not also completely uniform. Therefore, surface profiles having regularity or highly precisely defined surface profiles cannot be formed. In the cases of embossing and impressing, although production of molds may be difficult depending on shapes of convexes or concaves, they have an advantage that if a mold is once produced, surface convexes or concaves can be easily formed thereafter. However, the same surface convexes or concaves cannot necessarily be formed even with the same mold depending on properties of materials, pressures at the time of pressing and so forth, and it is difficult to form convexes or concaves with good reproducibility on any materials.
There are also proposed methods of producing light diffusing panels or microlenses by utilizing photolithography, which is a common technique in the manufacture of semiconductor devices and so forth, (Patent documents 2 and 3). In the technique disclosed in Patent document 3, a gray scale mask pattern is used to control thickness of resist to be solubilized by light exposure, and thereby produce microlenses having convexes of desired shapes. The gray scale mask is a mask in which light transmission distribution is formed by providing a pattern of tones, and a gray scale mask of which light transmission is controlled by changing size or numbers of apertures provided in the mask film is disclosed in Patent document 3.
Patent document 1: International Patent Publication WO2004/021052
Patent document 2: Japanese Patent Unexamined Publication (KOKAI) No. 2004-294745
Patent document 3: Japanese Patent Unexamined Publication No. 2004-310077